Ether lipids are widespread in nature, and they are structurally and functionally important components of membranes. The roundworm Caenorhabditis elegans synthesizes numerous lipid species containing alkyl and alkenyl ether bonds. We isolated C. elegans strains carrying loss of function mutations in three genes encoding the proteins required for the initial three steps in the ether lipid biosynthetic pathway, FARD-1/FAR1, ACL-7/GNPAT and ADS-1/AGPS. Analysis of the mutant strains show that they lack ether lipids, but possess the ability to alter their lipid composition in response to lack of ether lipids. We found that increases in de novo fatty acid synthesis and reduction of stearoyl- and palmitoyl-CoA desaturase activity, processes that are at least partially regulated transcriptionally, mediate the altered lipid composition in ether lipid-deficient mutants. Phenotypic analysis demonstrated the importance of ether lipids for optimal fertility, lifespan, survival at cold temperatures, and resistance to oxidative stress.